Influence of a Magnetic Field on Wave Motions in Thermally Unstable Photodissociation Regions

The propagation of waves in a thermally unstable medium with a magnetic field is considered. The characteristic perturbation growth and wave breaking times have been found in the approximation of weak nonlinearity and small deviations from adiabaticity; the wave profiles at the breaking time are presented. We show that the development of instability is suppressed as the wave propagation direction changes from longitudinal to transverse relative to the magnetic field. Our studies have been carried out for the atomic zones of photodissociation regions, for which we have previously determined the conditions for the development of an isentropic thermal instability mode.